A shit, having the consistency of toothpaste, that contains enough mass so as it stacks upon itself it will create a pile of shit in the toilet bowl that breaches the water level in the bowl. The pile of crap in the toilet will resemble a volcano. (Vesuvius is a famous volcano in Italy.)

I don't know what I ate for lunch, but by two o'clock I had dropped a vesuvius in stall # 2

A sex move where one takes an enema, does a handstand, and squirts diarrhea all over the other person/room/goat/etc. (For those that dont know, Mt. Vesuvius was the volcano that covered Pompeii in ash, desroying the city.)

A-So you have a date with Bianca tonight?
B-Yeah, I'm gonna take her back to my place and give her a Mount Veuvius.